Methods and devices for countering grativity induced loss of consciousness and novel pulse oximeter probes

ABSTRACT

Disclosed herein are methods and devices of obtaining plethysmograph readings and utilizing plethysomography to identify when pilots are about to experience GLOC. Furthermore, in other embodiments, the invention pertains to methods and devices designed to warn a pilot that he/she is about to enter GLOC and/or automatically averting catastrophic damage or injuries by directing a plane being piloted to take predetermined corrective actions. Specifically disclosed is a system embodiment for assisting in the prevention of gravity induced loss of consciousness. The system comprises at least one pulse oximeter probe  10  configured for securing to a central source site of a pilot and to generate signals indicative of blood flow at said central source site, an analyzer unit  58  communicatingly connected to said at least one pulse oximeter probe  10 , said analyzer unit comprising at least one processing module  56  configured to determine whether said blood flow is approaching a predefined level, and an aircraft computer  51  communicatingly connected to said analyzer unit  58 , said aircraft computer  51  comprising at least one processing module  59  configured to effect a predetermined reaction responsive to said blood flow falling below a predetermined level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of the Aug. 11, 2005, filing date ofU.S. provisional patent application No. 60/600,548.

BACKGROUND OF THE INVENTION

Gravity-induced loss of consciousness (“GLOC”) is a phenomenon thatoccurs when someone is subjected to substantially increasedgravitational loads (+Gz) for a sustained period. High-performanceaircraft, such as fighters, allow maneuvers that generate +Gz thatexceed the limits of the human body. This predisposes to GLOC and aserious degrading of physiological and cognitive performance. GLOC isone of the primary physiological threats to pilots and crews ofhigh-performance aircraft. Since the mid 1980s, one branch of the USmilitary, the United States Air Force, has lost 29 aircraft and 22pilots to GLOC. (The Effect of Negative Gz Recovery from GLOC onCerebral Oximetry, Broughton, presentation at USAF School of AerospaceMedicine, Brooks AFB, Texas (2003).) Similar loss rates can be expectedfor the other services flying high performance aircraft. In addition tothe loss of life, the cost of training and lost aircraft is staggering.

Almost loss of consciousness (ALOC) is even more common than GLOC.Symptoms include euphoria, apathy, displacement, depersonalization, poorresponse to auditory stimuli, immediate memory difficulties, sensoryabnormalities, motor abnormalities, confusion, and dream-like statewithout loss of consciousness, which are considered precursors of GLOC,which is defined as “A state of altered perception wherein one'sawareness of reality is absent as a result of sudden, critical reductionof critical blood circulation caused by increased G forces”.(Morrissette K L, McGowan D G. Further support for the concept of aG-LOC syndrome: a survey of military high-performance aviators. AviatSpace Environ Med. 2000; 71:496-500; Burton R R, G-Induced Loss ofConsciousness: Definition, History, Current Status. Aviat Space EnvironMed. 1988; 59:2-5.)

Some methods have been developed to increase G-level tolerances,including centrifuge training, weight training, the anti-G suit,positive pressure breathing, anti-G straining maneuvers and posturalmodification in the cockpit. The current capabilities of trainedindividuals to maintain clear vision during sustained exposures to +9Gz, an increase in protected +Gz tolerance of about +4 Gz over World WarII fighter pilots, is largely a result of combined use of a G suit andself-protective straining maneuvers such as the M-1, L-1 and pressurebreathing, all of which are variants of the Valsalva maneuver developedin the 1940s. (G-induced Loss of Consciousness and its Prevention, EarlWood, (1988) Mayo Clinic, Rochestor, Minn.) However, despite suchtraining, a review of ten fatal crashes attributed to GLOC shows thatsuch measures fall short of addressing the problem. Id. The Wood reviewnotes that the likely causes of such failures were: (1) increasedcapability of jet-powered fighters to sustain, with minimal piloteffort, accelerations in the 7-10 +Gz range for periods longer than thesymptom-free 3-8 second cerebral ischemic anoxic period which precedesGLOC, (2) an improperly performed Valsalva-type straining maneuver, and(3) development of a hypotensive vasovagal type reaction.

The inventors believe that currently used techniques do not adequatelyaddress the problem of GLOC (which for the purposes of this documentpertains to both ALOC and GLOC) because they ultimately put the burdenon the pilot to realize when he/she is about to sustain GLOC.

SUMMARY OF THE INVENTION

The subject invention pertains to methods, devices and systems ofobtaining plethysmograph readings and utilizing plethysomography toidentify when pilots are about to experience GLOC and for trainingpilots to recognize signs and symptoms of impending GLOC. Furthermore,in other embodiments, the invention pertains to methods and devicesdesigned to warn a pilot that he/she is about to sustain GLOC and/orautomatically averting catastrophic damage or injuries by directing theplane to take predetermined corrective actions. Finally, the subjectinvention allows measurements made during training in centrifuges andaircraft to be displayed for real-time feedback to teach the pilot tooptimize GLOC prevention maneuvers and to be stored and used to providean individual pilot's plethysmographic data for developing GLOC“profiles” which can be programmed into flight systems to determine whenan individual pilot is entering the early stages of GLOC based onpreviously collected data.

According to other aspects, the subject invention pertains to novelpulse oximeter probes. The term “pulse oximeter probe” as used hereinrefers to probes that can be used for pulse oximetry determination ofarterial blood oxygen saturation and/or used for plethysmography.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a pulse oximeter/plethysmographyprobe designed for securement in the nose of the user.

FIG. 2 shows a side cross-sectional view of the embodiment shown in FIG.1.

FIG. 3 shows a side view of a user having a pulse oximeter probe asshown in FIG. 1 inserted and secured in their nose.

FIG. 4 shows a side view of a pilot wearing a mask, having a pulseoximeter probe that interacts therewith.

FIG. 5 is a schematic of an embodiment of the subject invention thatcomprises an analyzer unit integrated with an aircraft computer.

FIG. 6 is a diagram showing a schematic of an embodiment of the subjectinvention comprising an analyzer unit operationally coupled to anaircraft computer.

FIG. 7 shows a perspective view of a pre-auricular reflectance probeembodiment of the subject invention.

FIG. 8 shows a side view of a pre-auricular reflectance probe embodimentof the subject invention.

FIG. 9 shows a perspective view of an alar pulse oximeter probeembodiment.

FIG. 10 shows a front perspective view of the alar pulse oximeter probeembodiment shown in FIG. 9.

FIG. 11 shows a rear perspective view of the alar pulse oximeter probeembodiment shown in FIG. 9.

FIG. 12 shows a bottom view of the alar pulse oximeter probe embodimentshown in FIG. 9.

FIG. 13 shows a plethysmograph obtained from the right and left cheek ofan individual. FIG. 13 a shows the right and left plethysmograph withoutdepressing the carotid artery. FIG. 13 b shows the right and leftplethysmograph with pressing the right carotid artery. FIG. 13 c showsthe right and left plethysmograph after releasing the right carotidartery.

FIG. 14 represents a plethysmograph from a pulse oximeter probepositioned on the cheek. The AC component (or cardiac component forpurposes of this example) is provided on the top and the DC offset (ornon-cardiac component for purposes of this example) is provided on thebottom. Pressing on the carotid diminishes blood flow, as seen in the ACcomponent (see arrow). Conversely, the DC offset goes up when thecarotid is depressed (see arrows).

FIG. 15 represents a plethysmograph obtained from the finger. The DCoffset is plotted at the top and the AC component at the bottom.

FIG. 16 represents a diagram illustrating a method embodiment of thesubject invention for obtaining a personalized data profile for anindividual with information for determining whether individual is aboutto enter GLOC.

FIG. 17 represents a perspective view of a post-auricular probeembodiment.

FIG. 18 represents a perspective view of an ear canal probe embodimentfor obtaining plethysmography readings from a user's ear canal.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS OF THE INVENTION

Turning to FIG. 1, a nasal pulse oximeter probe 10 is shown designed forthe comfortable placement in the nostrils of a human or non-human. Thenasal probe 10 may be made of a wide array of materials, including, butnot limited to, silicon, rubber, plastic or other polymer-basedmaterials, or other suitable materials. Preferably, the nasal probe iscomprised, at least in part, of materials (similar to hearing aid earmolds) that are soft and flexible as to allow proper comfort by theuser, but possess enough rigidity to properly conform to the inner wallsof the nose and provide frictional resistance to secure the probe in theuser's nose. The nasal probe 10 comprises a first insert 16 havingdefined therein a channel 15 and a second insert 18 having definedtherein a channel 17. Channels 15 and 17 are of a dimension to allow forthe free-flowing passage of air as the user inhales and exhales in andout of the user's nose. Positioned in or on the medial wall of insert 16is a light generating source, such as a light emitting diode (LED). Aphotodetector 14 is positioned on or in the medial region of insert 18.Wires 20 and 22 are connected to the light generating source 12 inphotodetector 14, respectively. To assist in the management of wires 20and 22, wires 20 and 22 may be secured together by fastener 24, such asa sleeve. Those skilled in the art will appreciate than any means forholding together wires may be used for this purpose, including, but notlimited to, a clip, tie, ring, band, etc.

In addition, the inventors do not intend to be limited to the type ofprobe that may be used. U.S. application Ser. Nos. 10/176,310;10/751,308; and 10/749,471 disclose various probe embodiments that maybe implemented for use in accord with the teachings herein. Theseapplications also teach the functional and technical aspects of the LEDand photodetector.

As used herein, the term “central source site” refers to a site above auser's neck, wherein information regarding blood flow at such sitecorrelates with blood flow to the user's brain. Examples of centralsource sites, include, but are not limited to, the tongue, lip, cheek,nasal nares, nasal septum, nasal alar, pre-auricular region,post-auricular region and ears.

FIG. 2 shows a cross-sectional side view of the nasal probe embodiment10 shown in FIG. 1. The LED(s) 12 and photodetector 14 are positionedacross from each other. To monitor oxygen saturation, two or more LEDsare typically required. For plethysmography, only one IR LED is needed.Further, without being limited to any specific mechanism or theory, itis the belief of the inventors that the plethysmogram will show signs ofGLOC far earlier than changes in oxygen saturation. However, it iscontemplated that the probes and methods of the subject invention may bedesigned and used to monitor both plethysmography and oxygen saturationof the user.

Insert 16 comprises a medial region 21 and a lateral region 25. Insert18 also comprises a medial region 23 and a lateral region 27. The user'snasal septum would lie in the space defined by the medial regions 21, 23of inserts 16, 18, respectively. Accordingly, the medial regionrepresents that portion of the insert that contacts the user's nasalseptum. The lateral region represents that portion of the insert that isproximate to the user's nares. Though the disclosed embodiment showsthat the inserts completely define an inner channel, with the inserthaving a medial region and a lateral region, the insert may be fashionedto define less than the full circumference around an inner channel.Wires 20 and 22 are connected to the LED 12 and the photodetector 14,respectively.

FIG. 3 shows a side view of a person having the nasal probe embodiment10 placed in their nostrils. Wires 20 and 22 are covered and fastenedtogether by a sleeve, which together form wire 32.

FIG. 4 shows a pilot 44 wearing a helmet 46 attached to a mask 40. Themask 40 comprises an air hose 48 attached to the mask compartment 43.The pilot has positioned in his nose 45 the nasal probe 10 shown inFIG. 1. Wire 32 containing wires 20 and 22 passes through hole 42defined in the mask compartment 43. It will be appreciated by thoseskilled in the art that the wire may be secured a number of differentways in the mask and/or air hose 48. For example, the hose 48 may have achannel defined therein through which the wire 32 may pass. Theembodiment shown in FIG. 4 would most likely comprise fastening the wire32 to the outside of the hose 48 so that it does not obstruct theactions of the pilot 44. The wire 32 carries the signals from thephotodetector to a signal processor and analyzer unit to be discussed infurther detail herein. It is important to reiterate that the probe usedin conjunction with the mask, nasal, cheek or otherwise, is not limitedto the embodiment specifically shown.

Turning to FIG. 5, there is shown a system 50 for processing signalsobtained from a pulse oximeter probe being worn by a pilot andconducting a reaction responsive to certain information received fromsaid pulse oximeter probe. The system comprises an analyzer unit 58 thatis configured to receive and process signals from lines 52 and 54. Thoseskilled in art will appreciate that the signals may be preprocessed tosome degree by a separate signal processor and subsequently sent as onesignal stream to said analyzer unit 58. Thus, the analyzer unit 58 isconfigured to receive signals from either lines 52 or 54 or acombination of both. The analyzer unit 58 comprises a processing module56 comprising software and/or electrical/circuitry components todetermine whether the signals received from the pulse oximeter probecorrelate to a loss in blood volume indicative of inducing GLOC. Theanalyzer unit 58 may also comprise a second processing module configuredto generate a warning signal.

During a typical high +Gz maneuver, a pilot is trained to take in amaximal deep breath as quickly as possible and to either hold it for ashort period of time while bearing down and then performing a rapidforced exhalation, or alternatively, to take in a deep breath and forcethe air out continuously against pursed lips. With either maneuver, theidea is to “trap” oxygenated blood in the head temporarily (3-5 seconds)and then rapidly allow the blood to return to the lungs. These maneuversare repeated at 5-10 second intervals throughout the high +Gz period. Itis both important to take in a maximal inspiration and then also to beardown and release the breath against resistance. Taking in a deep breathand bearing down forces blood to the head, but if the maneuver is heldfor too long, venous return to the heart is impeded, flow to the braindecreases and GLOC ensues. Thus, maneuvers to prevent GLOC are a “doubleedged sword” and must be performed correctly or they can actuallyexacerbate GLOC.

The disclosed system can be used during centrifuge and aircraft trainingto provide real time feedback via visual and/or auditory cues to helpthe pilot optimize these maneuvers. Additionally, when optimal maneuversare obtained, the system can store the plethysmogram that signals theonset of GLOC. This may be a system that evaluates the amplitude of thepre-+Gz plethysmogram and then recognizes when the plethysmographysignals have decreased by a predetermined percentage of the pre-+Gzvalue which is individualized for each pilot and determines when GLOC isimpending (as defined herein a pre-GLOC condition). Numerous factorsincluding the physical characteristics of the pilot influence theirability to withstand sustained +Gz loads. The individualized informationcan be loaded into a computer system that continually evaluates theplethysmogram (and therefore blood flow to the head) both during levelflight and during +Gz maneuvers and based on predetermined data candetermine that the pilot is about to experience forces and declines inblood flow to the head which will result in GLOC if the high +Gz load ismaintained. Previous research indicates that unconsciousness ensuesapproximately 5-8 seconds after cerebral blood flow (CBF) decreases by72-80% from baseline flow. (Florence G, Bonnier R, Riondet L, Plagnes D,Lagarde D, Van Beers P, Serra A, Etienne X, Tran D. Cerebral corticalblood flow during loss of consciousness induced by gravitational stressin rhesus monkeys. Neurosci Lett. 2001; 305:99-102.)

The GLOC warning system could be designed to evaluate the amplitude ofthe plethysmograph just as +Gz acceleration begins and monitor theamplitude of the plethysmograph during the +Gz maneuver. At a presetpercentage of the pre +Gz amplitude an alarm can be actuated. If thepilot does not respond to the alarm and the amplitude continues to droptowards the critical decrease in CBF (e.g., 65-85% below baseline flow)the autopilot could take control and decrease the +Gz load until theplethysmograph amplitude increases above a critical level.

Thus, according to another embodiment, as shown in FIG. 16, the subjectinvention pertains to a method of obtaining an individualized profileconcerning the amount of Gz load and duration likely to effect alowering of head blood flow of an individual to cause GLOC, the methodcomprising subjecting the individual to a Gz load increase gradient 900,monitoring the blood flow to the head through use of a pulse oximeter ata central location 910; determining the decrease of blood flow andduration of decrease blood flow that causes GLOC for the individual 920;obtaining a data profile for the individual 930; and loading the dataprofile onto an aircraft computer 940. The implementation of apersonalized data profile increases the accuracy of predicting when anindividual will undergo GLOC, and can therefore be used to better avertGLOC for the individual. In particular, the processing module containingthe data profile can establish a pre-GLOC condition for the individualthat when triggered will actuate an alarm and/or direct the aircraftcomputer to take corrective maneuvers. The terms “pre-GLOC condition” or“condition(s)” represent an empirically determined blood flow andduration conditions preceding GLOC for an individual, and likely to leadto GLOC, but which are established at a predetermined time sufficientlyin advance of GLOC so as to allow a pilot to react to avoid GLOC. Use ofthe personalized profile also will avoid unnecessary false alarms forthe individual, which will give the pilot more control over theaircraft, as the physiological conditions sufficient to induce GLOC willvary from pilot to pilot. The pilot can be subjected to Gz loads throughuse of a centrifuge, air flight maneuvers, or other Gz load producingmeans. The centrifuge is the most preferred means, as it can be closelycontrolled and monitored.

In an alternative embodiment, GLOC avoidance training can be implementedusing the methods of the subject invention. By closely monitoring thephysiological conditions leading up to GLOC for the individual pilot,each pilot can be trained to sense when they are about to enter GLOC andproperly react with the valsalva maneuver or other corrective actions.In a preferred embodiment, as part of the training process, the pilot isgiven a feedback signal to inform the pilot when he is entering apre-GLOC condition. This will assist in the pilot correlating internalfeelings and sensations associated with the pre-GLOC condition in orderto more quickly recognize the condition. Furthermore, as is discussed,infra, holding the valsalva maneuver too long can have acounter-productive effect. Utilizing the subject training methods willallow the pilot to practice and refine the optimal valsalva maneuvertechniques. Feedback signals may be implemented which will assist thepilot in properly timing the valsalva maneuver techniques.

Referring back to FIG. 5, in the system embodiment 50, the analyzer unit58 is shown as integrated into the aircraft computer 51. The aircraftcomputer 51 comprises a processing module 59 configured to automaticallyconduct a corrective flight maneuver with and/or without input from thepilot. The aircraft computer 51 is also connected to an alarm 55 that isactuated upon analyzer unit 58 sending a signal to said aircraftcomputer 51 indicating a predetermined low-level blood flow. In aspecific embodiment the detection and monitoring of changes in bloodflow comprises establishing a baseline value of plethysmography signalsunder normal Gz conditions, and then comparing later obtainedplethysmography signals to said baseline value. In a typical embodiment,the analyzer unit comprises a processing module configured to establishthe baseline value, continuously monitor the signals and compare to thebaseline value.

FIG. 6 shows an alternative embodiment system 60 for processing signalsobtained from a pulse oximeter probe being worn by a pilot andconducting a reaction responsive to certain information received fromsaid pulse oximeter probe. The system 60 comprises an analyzer unit 68is a stand-alone unit connected to wires 52 and 54. The analyzer unit 68is connected to an aircraft computer 61 through line 63 and directly toan alarm 65 through line 67. Upon the analyzer unit 68 determining lowblood flow, the analyzer unit 68 may actuate an alarm 65 in conjunctionwith sending the low blood volume signal the aircraft computer 61. Forthe sake of redundancy, the aircraft computer 61 may also connected tothe alarm 65 via wire 69. Like system embodiment 50, the aircraftcomputer 61 comprises at least one processing module (not shown)configured to conduct a corrective flight maneuver.

The alarm 55 or 65 may be visual and/or audible in nature, such as alight being actuated on the flight panel or a speaker sounding an alarmsuch as a buzzer. The aircraft computer may also comprise at least oneprocessing module for directing the plane to take corrective flightmaneuvers designed to unload the wings of the aircraft so as to decreasethe Gz loads on the pilot. One example of such a maneuver includes, butis not limited to, leveling the plane to a steady attitude and altitudedecreasing the pitch to level flight attitude. Another example includesimmediately leveling the wings while in a steep (60-90 degrees bankangle) high speed turn. The wings' level attitude is designed to induceblood flow to the brain.

The term “aircraft” as used herein refers to any type of craft designedfor traveling above the ground. Aircraft is also used in a broader anduncommon sense as to refer to any traveling vehicle that, by the natureof its speed, acceleration and maneuvering, generates force that mayinduce GLOC in the operator of such aircraft, including vehiclesdesigned for operation on the ground.

The term “wire(s)” as used herein refers to any structure havingconductive properties to carry electrical signals. The term wire also isused in an uncommon fashion to denote that the two structures the termwire is used to connect may be substituted by a wireless means oftransmitting electrical signals between the two structures.Alternatively, where wires are used to carry signals from the probes toanother component, such wires may be substituted with a wireless meansof transferring the signals. For example, conventionaltransmitter/receiver devices could be implemented in the probe and thecomponent to which the probe sends it signals.

The term “communicatingly connected” as used herein refers to anyconnection either via wires or wireless connection, that is sufficientto convey electrical signals to and/or from at least two components thatare communicatingly connected.

As used herein, the terms “signals indicative of blood flow” refers tosignals corresponding to blood volume changes in tissue caused bypassage of blood, i.e., signals indicative of perfusion or blood flow.See Murray and Foster, The Peripheral Pulse Wave: InformationOverlooked, Journal of Clinical Monitoring, 12:365-377 (1996).Typically, these signals are derived from a pulse oximeter probe whichproduces a waveform produced as a result of absorption of deliveredenergy (e.g. via a light source) by hemoglobin in red blood cells. Suchsignals are referred to herein as plethysmography signals.

The term “processing module” may include a single processing device or aplurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on operational instructions. Theprocessing module may have operationally coupled thereto, or integratedtherewith, a memory device. The memory device may be a single memorydevice or a plurality of memory devices. Such a memory device may be aread-only memory, random access memory, volatile memory, non-volatilememory, static memory, dynamic memory, flash memory, and/or any devicethat stores digital information.

Turning to FIG. 7, a pre-auricular reflectance probe 500 is shown. Thepre-auricular region is the region in front of the ear. This probe 500comprises a wiring harness 515 having at its distal end 511 a probe basestructure 510 and at its proximal end 512 a connector 520. Thepre-auricular reflectance probe embodiment 500 is designed to be securedaround the user's ear with the probe base structure 510 typicallysecured just in front of the tragus of the ear. The probe base structure510 may be flexible but is preferably rigid or substantially rigid, soas to not bend or deform during use of the probe 500. In a preferredembodiment, the wiring harness is made of a flex circuit such as, butnot limited to, those offered by Minco Products, Inc., 7300 CommerceLane, Minneapolis, Minn. 55432-3177 U.S.A. or NorthPoint Technologies,207 E. Park Ave., Mundelein, Ill. 60060. The connector 520 may be anysuitable connector so as to bring the wires of the wiring harness 515into electrical communication with a corresponding receptacle withanother wire connected to the analyzer unit, or directly onto areceptacle on the analyzer unit.

As shown in FIG. 8, the wiring harness 515 comprise wires 516 made of aconductive substance sufficiently insulated. Wires in the wiring harness515 are connected to the LED 514 and the photodetector 512 (e.g., aphotodiode) of the probe base structure 510. The wiring harness 515 maybe provided with an adhesive material 524 that assists with thesecurement of the probe embodiment in place around the ear and in frontof the tragus. Before securing the probe 500 in place, a peel-back layer525 is removed and the adhesive material 524 adheres the probe to theskin of the user.

The pre-auricular reflectance probe 500 is designed to obtainplethysmography readings and/or oxygen saturation measurements of thetemporal artery. The temporal artery is an ideal target since itdirectly branches off the carotid artery (which is the primary artery toone hemisphere of the brain). The LED 514 directs light to the temporalartery, and depending on the amount of blood flow, or oxygen saturation,the blood in the temporal artery will absorb a quantum of the emittedlight. Some of the light is reflected out from the temporal artery andsensed by the photo-detector 512. The amount of light reflected isdirectly correlated with the amount of blood and/or oxygen saturation ofthe blood present in the artery. The spacing between the LED 514 andphotodetector 512 is critical for obtaining accurate measurements. Thespace between the LED 514 and photo-detector 512 is typically in therange of about 5 mm to about 35 mm. Preferably, the space is in therange of about 10 mm to about 20 mm. The most preferred range is of thespace is about 12 mm to about 16 mm.

In an alternative embodiment, the subject invention is directed to aprobe embodiment similar to the pre-auricular reflectance probe, or justthe probe base structure with the at least one LED and photodetector,which is embedded into a pilot's helmet, such as in the padding of thehelmet. The probe is embedded into the pilot's helmet at a location suchthat the probe is positioned and stabilized at the pre-auricular region,upon placement of the helmet on the user's head. Accordingly, in atypical embodiment, the probe is embedded in the padding of a helmetthat covers or is proximate to the user's ear.

FIGS. 9-12 show a nasal probe embodiment 800 configured for obtainingplethysmography readings and/or oxygen saturation readings from theuser's nasal alar region. The nasal probe embodiment 800 comprises abase portion 813 which runs along the longitudinal ridge of the nose. Atthe distal end 833 of the base portion 813 is a bridge portion 819. Thebridge portion 819 runs transversely across the nose and comprises aright flap portion 812 at one end and a left flap portion 817 at itsleft end. The right and left flap portions 812, 817, respectively, arepositioned above the right and left nares of the user. The left flap 817has attached thereto or integrated therewith at least one LED 810 orother light source. Extending down from the right and left flaps 812,817 are a right extension 823 and a left extension 824. Attached to orintegrated with the left extension 824 is a wing fold 820 that isconfigured to be inserted into the user's left nostril. The wing fold820 has at its distal end a photodiode 825 attached thereto orintegrated therewith. The wing fold 820 is designed to bend over and beinserted into the user's nostril such that the photodiode 825 ispositioned directly across from the LED 810 located on the exterior ofthe user's nose. Extension 823 comprises wing fold 814 which is designedto be inserted into the user's right nostril. The positioning of wingfold 814 in the user's right nostril provides a counter force to thewing fold 820 which would tend to pull the probe 800 towards the left.Thus, the right flap 812, right extension 823, and right wing fold 814act together to assist in securing the nasal probe 800 in place. Asshown in FIG. 11, the nasal probe 800 is provided with an adhesivematerial 835 and a peel-back layer 830. Before use, the peel-back layer830 is removed and the adhesive 835 assists in securing the nasal probe800 to the skin of the user's nose. At the proximal end 834 of the base813, a connector 840 is provided. Wires 836 are provided in the nasalprobe embodiment and run from the LED 810 and photodiode 825 up toconnector 840. Furthermore, a flex circuit as described above may beattached to or integrated with the probe embodiment 800 so as to providethe necessary wiring to the LED 810 and photodiode 825.

Through use of the novel alar probe design described above, theinventors discovered an unexpectedly superior probe position on thelateral side of the nostril just behind the prominent part, which isreferred to as the fibro-areolar tissue. The inventors have surmisedthat this part of the lateral nostril is supplied by the lateral nasalbranch of the facial artery, but there are several branches (similar toKiesselbach's plexus found on the nasal septum). This position alsoincludes the branches of the anterior ethmoidal artery anastamose(lateral nasal branches), which is a branch off the internal carotid.Accordingly, the fibro-areolar tissue site is an unexpectedly optimalsite for positioned a probe for use to prevent GLOC. Thus, in apreferred embodiment, the alar probe 800 is dimensioned so thatplacement onto the fibro-areolar region is optimized for the user.

According to an additional embodiment, the subject invention pertains toa probe designed for obtaining readings from the post-auricular region.As shown in FIG. 17, the post-auricular region 1711 is the region behindthe ear. The posterior auricular artery is a small branch directly offthe external carotid. It runs posterior to the auricle and superficialto the mastoid process of the temporal bone. The proximity to theexternal carotid means that readings from the post-auricular region canprovide improved insight to carotid blood flow than a probe on theforehead. Additionally, since collateral flow is not likely at thislocation it gives a good indication of unilateral flow through thecarotid. The other immediate advantage is the superficial nature of theartery coupled with the relative thin layer of skin covering it. Theforegoing features, plus the fact that the solid temporal bone isdirectly below, make the post-auricular region an ideal site forreflectance monitoring.

Another distinct advantage of the reflectance monitoring at thepost-auricular region is the lack of venous blood to interfere withsaturation readings, as sometimes experienced with forehead models. Thethin layer of skin and strong pulsation from the artery allows forcorrect arterial saturations to be calculated. Other benefits includethe lack of hair and fewer sebaceous and sweat glands to interfere withreadings. Finally, the area behind the ear is easy to secure a probe toand it is normally out of the way of other devices. Thus, according toanother embodiment, the subject invention pertains to a post-auricularreflectance probe 1700 comprising an elongated body portion 1710. Theelongated body portion 1710 is curved to wrap around at least a portionof the user's ear. The elongated body portion 1710 comprises a distalend 1713 and a proximal end 1714. At the proximal end 1714, theelongated body has attached thereto or integrated therewith a probe basestructure 1715. The probe base structure 1715 comprises at least one LED1716 and at least one photodetector 1717. The at least one LED 1716 andat least one photodetector 1717 are connected to and in electricalcommunication with wires 1718. The wires 1718 may extend from the probebase structure 1715 and end in a connector 1719. The wires may be ofvaried length depending on the application. For example, the wires mayend at the proximal end 1721 of the probe base structure 1715, or mayrun for length out of the probe base structure 1715 and connect to theaircraft computer, or components thereof (e.g. signal processing unit,analyzer unit, etc.).

In an alternative embodiment, the subject invention is directed to aprobe embodiment similar to the post-auricular reflectance probe 1700,or just the probe base structure 1715 with the at least one LED andphotodetector, which is embedded into a pilot's helmet, such as in thepadding of the helmet. The probe is embedded into the pilot's helmet ata location such that the probe is positioned and stabilized at thepost-auricular region, upon placement of the helmet on the user's head.

According to an additional embodiment, as shown in FIG. 18, the subjectinvention pertains to an ear canal probe embodiment 1800 for obtainingplethysmography readings from the ear canal, and more specifically thetympanic artery. The probe 1800 is tapered to assist in placement in theear, but may alternatively not be tapered. The probe comprises an innerend 1810 which is inserted into the ear canal first, and an outer end1820. An LED is 1812 is provided on one side of the probe 1800 with aphotodetector 1814 provided on the opposite side. Those skilled in theart will appreciate that the spatial arrangement and placement of theLED 1812 and photodetector 1814 may optimized by routineexperimentation. Connected to the LED 1812 and photodetector 1814 arewires 1822 and 1824, respectively, which come together to form wire1816. Wire 1816 exits out the outer end 1820 via exit 1818. The probe1800 is similar to that described in U.S. Pat. No. 5,213,099, but isspecifically tailored and used to obtain plethysmography readings fromthe ear canal. The '099 patent teaches use of an ear canal probe toobtain oxygen saturation and pulse readings, but does not contemplate orteach use of plethysmography to monitor blood flow and as a method todiminish the risk of GLOC. The inventors have found that plethysmographyreadings are particularly advantageous in accurately monitoring bloodflow (or perfusion), and more accurately and quickly determiningpre-GLOC conditions.

Example 1

A pulse oximeter probe was positioned on the right cheek and left cheekof an individual. FIG. 13 a shows the right and left plethysmographreadings of the individual. At a point in time, the right carotid arteryof the individual was depressed thereby stopping blood flow. FIG. 13 bshows the effects of pressing on one carotid artery while monitoringfrom both cheeks. The amplitude of the signal from the right cheek probedramatically decreases (see arrow). FIG. 13 c shows that the when thecarotid artery is released, the plethysmography signal from the rightcheek spikes (hyperemic response, see arrow) and then returns to normalamplitude. During GLOC, the same or greater decrease in the amplitude ofthe plethysmograph would be experienced from any probe monitoring fromthe head. It is believed that the amount of Gz load sufficient to reduceblood flow to the brain, and/or induce GLOC, varies. By knowing whatpercentage of pre +Gz blood flow leads to GLOC in any individual pilot apersonal profile for the pilot may be produced that optimizes the alarmfor that individual.

Example 2

The inventors have developed a new processing of the plethysmographysignal such that important information may be extrapolated from thesignal. This novel processing reveals information not before realized tobe obtainable from a plethysmography signal stream. In the past, theplethysmography signal stream was typically obtained from a peripheralsite such as the finger, or other extremity. It is the inventors' beliefthat obtaining the plethysmograph from a central site lacks much of thebackground noise found in the plethysmograph from a peripheral site, andit is the obtention of this “less noisy” signal that eventually led tothe realization that information such as respiration rate and venouscapacitance can be extrapolated.

The raw signal stream obtained from a pulse-oximeter probe is related tothe amount of light from the LED that hits the photodetector of thepulse-oximeter probe. The magnitude of the signal from the photodetectoris inversely proportional to the amount of absorption of the lightbetween the LED and the photodetector (greater absorption results inless light exciting the photodetector). The absorbed light is due tomultiple factors, including absorption due to tissue, absorption due tovenous blood, absorption due to arterial blood, and absorption due tothe pulsation of arterial blood with each heart beat. Typically, the rawsignal from the photodetector is processed (e.g. removal of artifactsand autogain of the signal) and also separated into two components. Thetwo components are intended to be the time varying signals that arerelated to the beat-to-beat variations caused by the pulsation and flowof blood in the arteries (typically called the AC component), and theslowly varying components that is related to the other physiologic andphysical properties of the signal, typically called the DC component(including non-pulsatile arterial blood, pulsatile and non-pulsatilevenous blood and tissue and bone). The AC signal has been typicallycalled the plethysmography and the DC component overlooked.

The amplitude of the AC component contains information about the amountof arterial blood flowing past the detector. In order to correctlyinterpret this information, the AC and DC components must be separatedmore rigorously than in standard monitors. In particular, the pulsatilearterial component should contain only that information that relates tobeat-to-beat variations of the heart. The DC component should containthe other, lower frequency effects from physiology such as therespiratory effects, blood pooling, venous impedance, etc.) and physicalsensor changes (e.g. changes in the orientation of the probe, etc.).

According to one signal processing method embodiment of the subjectinvention, the effects of the individual heart beats in theplethysmograph is separated out from the other information, which isfundamentally a slightly different goal than conventional processing,which is basically to obtain an adequate AC component and discarding theDC component. Standard practice is to implement a DC removal techniquethat involves removing the DC component by a low pass filter. Thistechnique, however, does not sufficiently separate all of the data fromthe two sources of information. The subject processing method obtains ahigher fidelity signal, which is critical when dealing with precisemeasurements of variables for determining a pre-GLOC condition. In aspecific embodiment, the high fidelity AC component and the DC componentof the plethysmography signal (previously ignored by those in the art)are achieved by:

-   -   1) discretely picking the peaks and troughs of the signal        (improved noise/artifact rejection can be achieved by looking        for peaks and troughs that exist at the expected heart rate,        estimated by Fourier or autocorrelation analysis, or from past        good data)    -   2) finding the midpoints (or minimum values) between peaks and        troughs    -   3) extracting the DC component as the interpolated (and possibly        smoothed or splined) line that connects these midpoints (or        minimum values)    -   4) extracting the AC component as the raw signal minus the DC        component.

FIG. 14 represents a plethysmograph from a pulse oximeter probepositioned on the cheek. The AC component is provided on the top and theDC component is provided on the bottom. Pressing on the carotiddiminishes blood flow, as seen in the AC component (see arrow).Conversely, the DC component goes up when the carotid is depressed (seearrows). This confirms the inventors' beliefs of the physiologicalphenomenon that is represented in the DC component. That is, for thisexample, the DC component increasing demonstrates that there is bothless blood flowing to the cheek, and because only the artery in occludedbut not venous return there is low venous impedance. The effect is thatless blood is flowing to the check, but that blood is able to leave thecheck. Since there is less blood between the LED and photodetector,there is less absorption of the signal, resulting in a higher DCcomponent signal. By separating the AC and DC components the effects onarterial blood flow and venous return can both be evaluated, a desirablefeature when monitoring variables for GLOC.

Example 3

In FIG. 15, the DC component is plotted at the top and the AC componentat the bottom. A finger probe was initially placed at heart level and a“baseline” AC component amplitude was obtained. The individual performeda Valsalva maneuver similar to what pilots are taught to do duringsustained +Gz in order to prevent GLOC. However, the Valsalva was heldfor over 10 seconds and this resulted in a decrease in blood flow(reduction in AC component amplitude), a common problem causing GLOC(holding the positive pressure for too long).

Next, the individual placed his finger above the level of his head(while standing up). This results in the amplitude of the AC componentincreasing. This contradicts convention teaching regarding the ACcomponent, which would predict the exact opposite result anddemonstrates the effects of local vessel reactivity to a change inposition relative to the heart The AC component increases because thereis LESS venous impedance and more blood flow probably due to localvasodilatation in arterioles in the finger between the LED and thedetector and there is less venous blood in the finger as demonstrated bythe increase in the DC component. The individual again performed aValsalva maneuver and the blood flow (AC component) decreased and didthe DC component due to diminished venous return.

Finally, the individual held his hand below the level of his heart. Asthe present new understanding of the different components ofplethysmography signals would predict, the AC component decreasedbecause of increased venous impedance and a decreased pressure gradientbetween the arterioles and the venules and the DC component decreasedbecause there was more blood pooled on the venous side between the LEDand the photodetector. The same result as above occurred during theValsalva maneuver. Also note that there is a small, but detectable,decrease in the DC component with each Valsalva. The foregoing furtherdemonstrates that the DC component must be adequately separated in orderto obtain a highly accurate AC component signal and to demonstrateeffects of the venous side (i.e. venous return).

While various embodiments of the present invention have been shown anddescribed herein, it will be obvious that such embodiments are providedby way of example only. Numerous variations, changes and substitutionsmay be made without departing from the invention herein. Accordingly, itis intended that the invention be limited only by the spirit and scopeof the appended claims. The teachings of all patents and otherreferences cited herein are incorporated herein by reference to theextent they are not inconsistent with the teachings herein.

The invention claimed is:
 1. A method of monitoring blood flow status tothe head of an individual, said method comprising: securing a pulseoximeter probe to a central source site of said individual, generating aplethysmography signal stream indicative of blood flow at said centralsource site; isolating an AC component signal stream and a DC componentsignal stream from said plethysmography signal stream with a signalprocessor; determining changes in blood flow at said central source sitebased on said DC component signal stream, and optionally said ACcomponent signal stream, with said signal processor; effecting with acomputer a predetermined reaction responsive to said blood flow fallingbelow a predefined value.
 2. The method of claim 1, wherein saidreaction comprises generating an alarm.
 3. The method of claim 2,wherein said alarm is a visual, tactile or audible warning.
 4. Themethod of claim 1, wherein said reaction comprises directing the flightcontrol systems of said aircraft to undertake a corrective flightmaneuver.
 5. The method of claim 1, wherein said determining changes inblood flow comprises establishing a baseline value of plethysmographysignals and comparing subsequently obtained plethysmography signals tosaid baseline value.
 6. The method of claim 1, wherein said AC componentsignal stream is isolated from the said plethysmography signal stream byidentifying peaks and troughs of said plethysmography signal stream;identifying minimum values or midpoints between said peaks and troughs,wherein an interpolated line connecting said midpoints or minimum valuesrepresents said DC component signal stream; extracting said DC componentsignal stream from said plethysmography signal stream; and obtainingsaid AC component signal stream.
 7. The method of claim 1, wherein saidindividual is a pilot during operation of an aircraft.
 8. The method ofclaim 1, wherein changes in blood flow are determined based on changesin the AC and DC component of said plethysmography signal stream.
 9. Asystem for monitoring blood flow status to the head of an individualcomprising an analyzer unit communicatingly connected to at least onepulse oximeter probe configured to generate a plethysmography signalstream at a central source site, said analyzer unit configured toisolate an AC component signal stream and a DC component signal streamfrom said plethysmography signal stream and to determine whether bloodflow is approaching a predefined level based on said DC component signalstream, and optionally, said AC component signal stream, and a computercommunicatingly connected to said analyzer unit, wherein said computercomprises at least one processing module configured to effect apredetermined reaction responsive to said blood flow falling below apredetermined level.
 10. The system of claim 9, wherein said reactioncomprises the generation of a visual alarm, tactile alarm, audiblealarm, or both.
 11. The system of claim 9, wherein said computer is anaircraft computer.
 12. The system of claim 11, wherein said analyzerunit is integrated into said aircraft computer.
 13. The system of claim11, wherein said reaction comprises directing said aircraft flightcontrol system to undertake a corrective flight maneuver designed tolessen or reverse gravity force inflicted onto said pilot.
 14. Thesystem of claim 11, wherein said analyzer unit is separate from theaircraft computer.
 15. A method of monitoring blood flow status to thehead of an individual, said method comprising: isolating an AC componentsignal stream and a DC component signal stream from a plethysmographysignal stream with a signal processor; and determining changes in bloodflow to the head of an individual based on said DC component signalstream, and optionally said AC component signal stream, with said signalprocessor.